Die rolling



Sept. 11, 19 H. N. ANDERSON DIE ROLLING Filed April 16, 1956 fie. 2

United States Patent 3,053,126 DIE ROLLING Harold N. Anderson, 21213 Aberdeen Road, Rocky River, Ohio Filed Apr. 16, 1956, Ser. No. 578,516 5 Claims. (Cl. 8016) The present invention relates to die rolling and more particularly to the art of forming gear teeth on gear blanks by rolling a die of gear form, rack, bevel, cylindrical or crown, etc., and a plastic or malleable gear blank together under pressure. The formation of gear teeth on suitable blanks by die rolling is described in several United States patents heretofore issued to me and the present invention is an improvement on the methods and die rolls described therein.

The art of rolling gear teeth on blanks by the use of die or die roll of gear form, rack, cylindrical, bevel or crown, etc., is based upon the principle that since two gears one of which may be of rack form having properly constructed teeth roll together at a definite uniform velocity ratio it follows that if one such gear and a plastic or malleable blank are rolled in contact at an appropriate relative velocity and an appropriate relative feed movement effected .therebetween, the teeth of the gear will form teeth on the blank and thereby transform the blank into a gear.

In the formation of gear teeth by rolling a plastic or malleable blank against a suitable die the teeth on the blank are generated and the teeth produced are theoretically truly a counterpart of or conjugate to those of the die. That is, if the teeth of the die have true involute form the teeth generated by them on the blank will theoretically have a true involute form. I have discovered, however, that dies of the character mentioned will not produce theoretically correct conjugate or counterpart tooth forms in gear blanks and that it is necessary to use a die having teeth modified from the theoretically correct form to produce a theoretically conjugate form on the blank. In other words, if it is desired to produce on a gear blank teeth having a theoretically correct involute form it is necessary to use a die, the teeth of which have a modified involute form. A departure in the die teeth from the theoretical conjugate form for the gear to be produced is necessary to compensate for the deformation, fiow and other characteristics of the material of the blank, and its different behavior characteristics under the different conditions which may prevail during the rolling operation. For example, blanks of the same material may be rolled at different temperatures thereby having different deformation, compression, flow or slip rates and requiring teeth of different nonconjugate form on the die roll to produce the same desired or predetermined form on the blank.

I have further discovered that the form of the teeth of the die roll must be such as to work the addendum and dedendum of the teeth being produced a greater amount than they would be worked if the teeth of the die roll were of theoretically counterpart form or correct conjugate form to the desired tooth form to be produced.

The object of the invention is, as suggested, the provision of a novel and improved method of producing by so-called die rolling gear teeth of correct desired form on a gear blank, and more particularly, an alloy steel, titanium or other like material, blank by rolling under pressure and in predetermined timed relation a suitable blank with a die having gear teeth thereon the form of which is modified from the theoretically correct form conjugate to the form of tooth which is is desired to produce, by having prominence above and below the pitch line, and the expression nonconjugate will hereinafter be used to designate such forms.

Further objects and advantages of the present invention will be apparent to those skilled in the art to which it relates from the following description wherein reference is made to the accompanying drawings forming a part of this specification, in which similar reference characters designate corresponding parts, and in which:

FIG. 1 is a fragmentary elevational view with portions shown in section of a die rolling machine provided with a die embodying the present invention;

FIG. 2 is a side view with portions in section of the die shown in FIG. 1;

FIG. 3 is a diagrammatic view showing the relative shape of the teeth actually employed on the die and their theoretically correct form conjugate to form being produced; and

FIG. 4 is a view similar to FIG. 3 but of a spur gear type die roll embodying the present invention.

Since involute gears are used almost exclusively, the present invention will be described as it applies to such gears, it being understood, however, that the invention is equally applicable to other known systems of gearing. The faces of the teeth of involute gears have the form of an involute curve evolved from a base circle. The teeth, therefore, have more or less curvature according to the number of teeth in the gear, for example, the teeth of an involute gear having 15 teeth will have a very pronounced curvature while the teeth of a gear of the same diametrical pitch but having 150 teeth will have a slight curvature and the teeth of a similar gear having 300 teeth will have almost no curvature. The faces of the teeth of a gear rack have no curvature. The gear rack is a sequel of the fact that the larger the number of teeth in a gear of any given diametrical pitch the larger will be its base circle, and that the nearer the base circle approaches a straight line the straighter are the faces of the teeth. A rack, in fact, is often referred to as a gear having an infinite number of teeth of uniform diametrical or circular pitch formed on a base circle of infinite radius. A crown gear is in effect a circular rack and its teeth have, or are, universally formed with flat faces. The word gear as hereinafter used, unless otherwise qualified, comprehends, not only cylindrical, and bevel gears etc. but also racks and crown gears or racks.

Because of the ease with which straight-sided teeth can be formed as Well as other reasons, it is desirable to have straight-sided teeth on the die and I have discovered that the addendum and dedendum of the teeth being formed can be worked in a desired manner and to the desired extent to produce teeth of theoretically correct involute form by using, in the case of the production of beveled gears, a die of bevel gear form and of a diameter lessthan twice the pitch cone length, the teeth of which, however, are straight-sided similar to the teeth of a crown gear. This produces a die of modified bevel gear construction the teeth of which will have prominence as referred to and which will produce the desired result.

The degree of modification or prominence required depends upon the material, temperature, etc. of the blank and can be attained by varying the bevel angle of the die. In the case of a die of spur gear form a similar or comparable modification or adjustment can be obtained by decreasing the diameter or size of the spur gear type die while maintaining the theoretically correct diametrical and circular pitches.

Referring particularly to FIG. 1 of the drawings, 10 designates a holder in which is carried a bevel gear blank B. The rolling of teeth 11 on the blank has been completed but the bevel gear type die D is still in position with its teeth 12 embedded in the blank. The blank is' Patented Sept. 11, 1962' held in the holder by a circular block 13, which serves not only this purpose but also as a shroud to limit the lateral flow of metal toward the center of the blank as the teeth are formed. The holder has an annular extension that acts as a shroud to limit the lateral flow of metal at the outside of the blank. The block 13 has a conical face which preferably, though not necessarily, coincides with the pitch cone of the finished gear. The block 13 is pressed into the blank and the blank thereby held in the holder 10, by a block '16 having a conical face coinciding with the pitch cone of the bevel gear type die D. The holder 19 is mounted on a shaft which rotates on an axis indicated by the center line and the die D is mounted to rotate on an axis indicated by the center line 26, while the holder and die are compelled to maintain a fixed speed ratio by timing gears not shown.

In addition to being rotated in timed relation to effect a relative progression of the die D about the blank B, the die and blank are moved or oscillated to and fro about their axis so that the respective die and blank teeth alternately approach each other in opposite directions. This oscillation is greater in one direction than in the other with the result that there is a relative progression or rolling of one about the other.

While the heated blank is being inserted in the holder 10 the block 16 and die D are withdrawn a suitable distance, and after the blank is in place the block 13 is inser-ted in the blank and the block 16 brought up into contact with it. The machine is then started to rotate the die and holder, and the die advances toward the blank until its teeth have sunk into the blank to the required depth, thus generating teeth on the blank.

The machine parts thus far described or refer-red to, or similar parts, are shown, together with the manner in which they are supported and operated, in my Patent No. 1,460,528, which is one of the patents previously referred to. It is to be understood that the foregoing description is only for the purpose of illustration and that the machine described and shown in said patent is by no means the only or even the preferred machine with which the present die may be employed or the present method practiced.

According to the theory of involute gears the faces of the teeth of the die D shown, which is of bevel gear form, should be slightly curved. The faces of the teeth, however, are flat, that is, similar to those of the teeth of a crown gear, from which it follows that theoretical teeth generated with the die D would not be truly involute or conform strictly to the involute principle. Beginning at the pitch line, where they will be of the correct thickness, the generated teeth should be relieved, that is, slightly thinner, both above and below the pitch line than they would be were they generated with a die having teeth of truly involute tooth form. The theoretical modification or divergence of the generated teeth from the true involute form should be equal to the degree of prominence of the faces of the teeth of the die, that is, their variation from their theoretically correct involute form. This can be better understood by reference to FIG. 3 where the form of the teeth of the die D having fiat faces b, c is superposed on a tooth shown in dot-dash lines having the corresponding theoretically correct involute form. Both teeth have the same pitch line thickness. This illustrates, exaggeratedly, the difference between the teeth of the die D and the shape the teeth would be if they were truly involute and conjugate to the tooth form which it is desired to produce on the blank B.

Since the teeth generated on the blank theoretically are conjugate or counterpart to the die teeth, teeth generated with the die D shown would be as much thinner than true involute teeth, above and below the pitch line, as the faces of the die teeth are promiment, that is, project beyond the true involute tooth form. This, however, is not true in actual practice particularly where lalloy steel, titanium and like blanks are employed. Because of the characteristics of the metal of the blank, including its compression, deformation or flow rates, etc., its behavior under the rolling action to which it is subjected is such that the teeth of the blank are not actually worked to their theoretically correct form. There is, so to speak, a lag in the flow or deformation of the metal which makes it necessary to work the metal of the addendum and dedendum of the teeth of the blank, that is, above and below the pitch line, a greater amount than would be theoretically required. In the present instance this is accomplished by the prominence on or of the faces of the teeth of the die mentioned above and the additional work performed on the addenda and dedenda of the teeth of the blank is complementary to, or a function of the amount of prominence of the faces of the die teeth. The degree of prominence required, as can be readily appreciated by those skilled in the art to which the invention relates, is a function of the rolling characteristics of the material of the blank and the temperature at which it is rolled, etc., and can be varied in the die by changing the bevel angle of the die while maintaining the faces of the teeth flat, or similar to those of a crown gear. As previously suggested, it is not necessary to form theoretically correct teeth on the blank, for example, teeth having so-called localized bearings may be produced in accordance with the present method by supplementing the previously mentioned prominence of the faces of the teeth of the die by an additional prominence suflicient to produce the desired localized bearing.

In the method of rolling shown in FIG. 1, shrouds are employed to limit the lateral flow of metal during the tooth-forming process and during the operation the die teeth enter pockets in the blank. In order to facilitate the repeated entrance and withdrawal of the die teeth into and out of the pockets, the ends of the teeth of the die are preferably beveled to provide teeth draught.

. This modification of the teeth not only facilitates separation of the teeth of the die from the interdental spaces in the blank but it improves the action of the die generally and reduces the amount of power required.

A prominence of the character referred to above can be obtained with die rolls of spur gear form by merely decreasing the size of the die while maintaining the same diametrical and circular pitches. If the size of the die is decreased, theoretically the curvature of the teeth increases, therefore, the degree or amount of prominence increases. Similar prominences may be obtained on the teeth of gear-like dies by means other than the employment of straight-sided teeth, but the teeth of such gear type dies would be curved and curved forms are less desirable since they are more diflicult to produce and maintain.

In the case of dies of gear form having flat faced teeth, the teeth can be readily cut by conventional methods regardless of whether the dies are of spur, helical, bevel including hypoid or any other gear form. After the dies are made and the teeth cut they can be readily hardened and subsequently ground. The upkeep of the dies is simply a matter of regrinding the teeth from time to time as they wear.

During the rolling operation the dies are preferably maintained at a temperature cool enough to prevent their temper from being drawn by having a stream of water played on them with the result that it is never necessary to reharden the dies.

From the foregoing it will be apparent that the objects heretofore enumerated and others have been accomplished and that there has been provided a novel method of producing gears having teeth of correct form, involute or otherwise, by rolling a suitable blank against a die of gear form but having its teeth modified by prominence from the form which is theoretically conjugate to the gear tooth form being produced. While the preferred embodiments of the invention have been described in some detail, the invention is not limited to the particular constructions shown and described and it is my intention to hereby cover all adaptations, modifications and uses thereof which come within the practice of those skilled in the art to which the invention relates and the scope of the appended claims.

Having thus described my invention, I claim as follows:

1. The method of producing metal gears having generated teeth of predetermined tooth forms which comprises rolling together under pressure a metal gear blank and a die of gear form having teeth, the thickness of which above and below the pitch line is greater than that of teeth conjugate to the gear which is to be produced.

2. The method of producing metal gears having generated teeth of predetermined tooth forms which com= prises rolling together under pressure a metal gear blank heated to a plastic state and a die of gear form having teeth of a form which is modified from the theoretical form truly conjugate to the form of the teeth being produced by having prominence above and below the pitch line.

3. The method of producing metal gears having generated involute teeth which comprises rolling together under pressure a metal gear blank and a die of gear form having teeth modified from the theoretical form conjugate to the form of teeth to be produced by having prominence above and below the pitch line.

4. The method of producing metal gears having generated involute teeth which comprises rolling together under pressure a metal gear blank heated to a plastic state and a die of cylindrical gear form having straightsided teeth modified from the theoretical form conjugate to the form of teeth to be produced by having prominence above and below the pitch line.

5. The method of producing metal beveled gears having generated involute teeth which comprises rolling together under pressure a metal gear blank heated to a plastic state and a die of beveled gear form having straight-sided teeth modified from the theoretical :forln conjugate to the form of teeth to be produced by having prominence above and below the pitch line.

References Cited in the file of this patent UNITED STATES PATENTS Anderson July 8, 1924 OTHER REFERENCES Practical Gear Design, Dudley, page 238, 1954. Gear Design and Production, Trautschold, pages 200,

201, and 203, 1955. 

